in reply to Data structure challenge

I've been thinking about this. Obviously, this is do-able in C (and similar languages), as you have C-like pseudo-code in your challenge. But, other than sparse arrays1, what would be practical benefit of this data structure be? If you add in a hashing function to map strings to your set of i, you still have the collision issue.

Are you considering this as a possible implementation of the arrays Perl's hashes use? It would seem kinda wasteful to add an indexing array just to avoid clearing and initializing in O(n) ...

1 I say sparse arrays because in the 2-array method, U doesn't have to be the upper limit of all i. It simply has to be the upper limit of how many i you can have at one time. So, if you know you'll only ever have a max of 10 things, they could be in the set of 2**32, but you would only need 2 10-element arrays and a short as your C.

------
We are the carpenters and bricklayers of the Information Age.

Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.

Replies are listed 'Best First'.
Re: Data structure challenge
by Abigail-II (Bishop) on Mar 18, 2004 at 14:24 UTC
    But, other than sparse arrays1, what would be practical benefit of this data structure be?
    Worst-case constant time operations, regardless of how many elements there are in the data structure.
    If you add in a hashing function to map strings to your set of i, you still have the collision issue.
    Well, yes. Don't do that then. ;-) As I said, it only 'works' if you know certain things about your set - in this case, you know you are only going to store non-negative integers not exceeding U.
    Are you considering this as a possible implementation of the arrays Perl's hashes use?
    No.
    I say sparse arrays because in the 2-array method, U doesn't have to be the upper limit of all i. It simply has to be the upper limit of how many i you can have at one time. So, if you know you'll only ever have a max of 10 things, they could be in the set of 2**32, but you would only need 2 10-element arrays and a short as your C.
    In the 2-array method I described, it's essential U is the upper limit of all i, because i is used as an index in the array A.

    Abigail

[reply]

In Section Meditations